The present invention generally concerns hot melt adhesives and coatings. More specifically, the present invention is directed to a transparent or pigmented film from a specific polyamide copolymer and/or terpolymer resin having characteristics making such resin suitable for use as a hot melt fabric adhesive, fabric patch adhesive, adhesive for other materials, or as a coating for a large variety of different materials.
In the prior art certain polyamide or nylon resins have been attempted for use as bonding materials for delicate synthetic fabrics, which characteristically have a relatively low melting point. Polyamide hot melt adhesives have been thought to be desirable for this purpose because of their correspondingly low melting points. In other words, with polyamide hot melt adhesives it would not be necessary to heat the adhesive to a temperature above the degradation temperature of the fabric in order to achieve a secure bond.
However, polyamide adhesives have had a number of disadvantages associated therewith. Because of their inherent stiffness, polyamides have been available for use as hot melt fabric adhesives generally only in web form or in powders. Powders have been messy, wasteful and difficult to use, with the consumer often using too much or too little adhesive for the particular adhesive application concerned. Webs of polyamide adhesive, while not as stiff as a solid film would be, generally have been unsatisfactory to use, because of the reduced amount of adhesive per unit area due to the presence of holes in the web. This debilitating characteristic has resulted in greatly reduced peel strength with correspondingly weak bonding of fabric to fabric.
One particular resin has been proposed by those skilled in the art as a hot melt film adhesive for bonding fabrics where the susceptability of the fabric to thermodegradation precludes the use of conventional higher melting adheives. Such proposed resin is a polyamide copolymer and/or terpolymer consisting essentially of the polyamide condensation product of: (a) laurolactam monomer in amounts of 80% to 20% by weight of the composition; and (b) a co-condensible monomer member selected from the group consisting of caprolactam, hexamethylene diamine adipate, hexamethylene diamine sebacate, and mixtures thereof in amounts of 20% to 80% by weight. Examples of such laurolactam containing polyamide copolymers are given in U.S. Pat. No. 3,515,702.
The melting point of the laurolactam containing resin utilized in the method of the present invention is in the range of approximately 240.degree. F., which has been shown to be satisfactory for bonding the vast majority of fabrics without heat damage thereto. However, heretofore by prior art methods, it has not been possible to make a transparent film of such resins with all their attending advantages. Prior art techniques, including the extrusion technique of film forming, have resulted in a foggy, cloudy and unattractive film of these otherwise suitable laurolactam containing resins. This has substantially reduced, if not completely destroyed, their utility as fabric adhesives for many applications. That is the fact because a cloudy or foggy film, especially when used to bond delicate fabrics, will show through the fabric and can be seen around the edges of the bond. This factor substantially detracts from the attractiveness of the clothing article or other article being bonded. Pigmented films of such resins have likewise been foggy and unattractive, which has considerably reduced their utility for label and applique application. Accordingly, such laurolactam containing polyamide resins in the prior art have been substantially lacking in utility for a number of bonding applications in spite of their other favorable characteristics, such as pliability, exceptional resistance to dry cleaning solvents, and good launderability in the normal laundering range of temperatures.
Accordingly, it is an object of the present invention to provide a film containing all the advantages of such resins, which film is transparent, to provide thereby utility in applications of fabric bonding.
It is an additional object of the present invention to provide a film of such laurolactam containing resins for yet further applications, which applications include the use of pigmentation.
Yet a further object of the present invention is to provide a film, transparent or pigmented, which possesses characteristics giving it utility for use in such applications as the coating of various materials.
It is yet an additional object of the present invention to provide a film, transparent or pigmented, of such laurolactam containing resins which is esthetically suitable for the imprinting of visual indicia on the surface thereof.
It is an additional further object of the present invention to provide a method of producing a transparent film from such laurolactam containing polyamide resin particles, said film being useful as a hot melt adhesive for fabric and other materials and as a surface coating for a variety of other materials.
It is yet a further object of the present invention to provide a method of producing a transparent film of such laurolactam containing polyamide resin particles, said method comprising drying said particles, extruding and heating said resin at temperatures sufficient to drive off monomer contaminants but not sufficient to degrade the resin, forming a film of molten resin and dropping the film onto a substrate backing means, and rolling said film to a uniform thickness.
It is yet a further additional object of the present invention to provide a method for forming a transparent film of such laurolactam containing resins by extrusion wherein the extrusion temperatures are maintained above approximately 350.degree. F., but below approximately 420.degree. F.
It is also yet a further additional object of the present invention to volatilize and drive off unreacted monomers in such raw laurolactam containing resins during the extrusion and heating thereof.
It is yet a further additional object of the present invention to provide a method whereby a concentration of such resins and a pigment is prepared and added prior to heating and extruding said laurolactam containing resin.
These and other objects and advantages of the present invention are accomplished by means which are set forth more fully with reference to the following drawing: